The present invention relates to new devices for injecting current into the line circuit of a telephone set and more particularly a hybrid injection circuit associated with a closed-loop detector. The new devices proposed by the present invention may be used advantageously in entirely electronic telephone exchange systems where, by means of thorough miniaturization, the operator's console contains all equipment formly placed in the desk and racks. Such concentration into a single console requires both miniaturization and the elimination of noise. In addition, the use made of electronics requires in certain cases small electrical order currents.
The subject of the present invention is a ringing current injection device having the following advantages: miniaturization, especially of the hybrid circuit, integration of the ringing current injector and protective resistors on this hybrid circuit, the elimination of switching relay noise by the use of electronics, and the considerable reduction of the current compared with that controlling earlier devices.
The purpose of the device according to the invention is to inject ringing current into the telephone set line when the order to do so is received by the central unit and depending on the status of the called telephone set, with interruption of this ringing current if the telephone set goes off-hook. This device therefore consists essentially of a circuit constituted around a central ringing current control component fed with signals from the central unit and closed-loop detector. This circuit is entirely electronic.
In order to explain more easily the technical characteristics and advantages of the present invention, a practical example is described below, it being understood that this example is not limiting with regard to its implementation and any possible applications.